A combination of a law enforcement agency and intelligence agency, the FBI is committed to fight against organised crime and terrorism within the United States. The FBI would have been responsible for surveillance of the men suspected of the hijackingson 11 September. Founded in 1908, the FBI grew to prominence during the fight against organised crime in the 1920s. At any one time the FBI is looking for 12,000 fugitives from justice.

Budget: $3.57 billion

Staff: 11,400 special agents and 16,000 support personnel

Biggest past failure: The 'war' against drugs

CIA - Central Intelligence Agency

Functions as an independent source of foreign intelligence to the US government. Its mission is to 'collect, evaluate and disseminate' information to help safeguard US national security. Originally backed bin Laden and other mujahideen in the struggle against the Soviet Union's occupation of Afghanistan, which began in 1979. After the collapse of Communism in 1989 and the Gulf war of 1991, Islamic fundamentalism became the agency's main target.

Set up in 1919 to combat the perceived threat from German spies. The lion's share of the work of the internal security service is now taken up with the fight against terrorism in Northern Ireland. It also provides intelligence about organised crime and international terrorism. In alliance with the FBI, it keeps tabs on Britain's Islamic community and would have provided the Americans with intelligence about any British links to Osama bin Laden.

Budget: Combined £713m with MI6 and GCHQ

Staff: 1,900

Biggest failure: IRA Bishopsgate and Canary Wharf bombings

MI6 - Secret Intelligence Service

Gathers information and recruits agents abroad, although it is often accused of operating in Northern Ireland and the British mainland. Began life as an offshoot of the domestic intelligence service, but became an independent service in 1922. Traditionally far more active in the Middle East than the CIA due to Britain's colonial history and must take some responsibility for the present instability of the Arabian peninsula and Yemen in particular.

Budget: Combined £713m with MI6 and GCHQ

Staff: 1,600

Biggest failure: Suez

FRANCE

DST - Directorate of Territorial Surveillance

Created in 1944 to combat economic and political espionage internally, and prevent terrorism. It also has a strong anti-industrial espionage responsibilities, after its role was secretly redefined in 1993. Earlier this year the DST apprehended Zacarias Moussaoui, a French Algerian, who had taken flying lessons in Boston. His dossier was passed on to the FBI, who ignored it. The DST repeatedly warned US intelligence and the FBI that bin Laden's organisation was training pilots at its camps. Maintains a very low profile.

Staff: 1,700

Budget: £38m

Biggest failure: Didn't arrest Carlos the Jackal when agents raided the house he was in.

DGSE - General Directorate for External Security

Part of the Ministry of Defence, the DGSE is responsible for military intelligence as well as for strategic information, electronic intelligence, and counterespionage. It was formed by amalgamating varied intelligence services after World War II. Strong presence in Algeria and the Middle East.